The investigation of the plasma kinin assay was continued. Topics involved in study included alternative methods of plasma preparation, alternative methods of separation of bound from free antigen, specificity, buffer system, surface adherence, purification of tracer, modification of volume, statistics, and assay parameters. The problems with the lack of specificity and with the low antibody affinity for bradykinin could not be overcome. An acceptable plasma kinin assay will await the production of new antibody. The dog hind limb bioassay for kinin was examined. Specificity of the vasodilatation response could not be shown to be due to bradykinin alone. Neither vasoactive monoamines nor acetylcholine appeared to be responsible for the nonspecific responses. Finally chromogenic kallikrein substrate suggested to be a bradykinin receptor blocker was examined in the dog hind limb. No effect on vasodilatation was observed. In another experiment a protein inhibitor was examined as a possible kallikrein antagonist. While the inhibitor is small, nonimmunogenic, and can enter cells, its potency as a kallikrein antagonist is too low to be of practical use currently.